Why does my cable box keep randomly changing the channel to NBC throughout the day and after daily updates?

I was just watching CNN and having missed a story I rewound it to the point I needed (about 3 minutes back).  I hit play and instead of playing the CNN feed that had been on for over an hour, it automatically changed channels to NBC's feed, thus erasing my ability to see what I wanted.  This random switching to NBC (a Comcast company owned channel) happens often and also after every single daily update.  It is never any other channel other than NBC.  I am [Edited: "Language"] that I couldn't see the news item and have no idea if it will replay.  The DVR is supposed to allow for such things. But on top of that the reset to NBC after every single daily update as well as random instances is rather suspicious considering the Comcast/NBC connection.